The proposed inter-disciplinary research plan combines molecular, biochemical, genetic, human pathologic, and animal functional studies to characterize a pro-metastatic regulatory network that has been found to regulate metastatic progression by a broad range of melanomas representing diverse mutational subtypes. Our published work has revealed that in the majority of human melanomas, over-expression of three pro-metastatic microRNAs (miR-1908, miR-199a5p, and miR-199a3p) drives metastatic colonization through direct targeting of ApoE gene and the heat-shock factor DNAJA4 (Pencheva et al., Cell, 2012; Pencheva, Buss et al., Cell, 2014). ApoE and DNAJA4 were found to robustly suppress metastatic colonization and angiogenesis. Our extensive previously published and unpublished work supports a robust and clinico-pathologically validated role for these genes and their network in human metastatic progression. Since our original publications, independent investigators have provided further support of a role for ApoE in cancer progression by demonstrating that the ApoE gene suppresses breast cancer metastasis and that the human ApoE4 polymorphism increases the likelihood of death from malignancy in men and women. These findings as a whole establish ApoE as a potent and dual regulator of metastatic progression and tumor angiogenesis. Thus, an enhanced understanding of the upstream mechanisms that regulate ApoE in cancer, its downstream mechanism(s) of action on tumor angiogenesis, its therapeutic potential, and the impact of ApoE polymorphic variants on cancer is required. The current proposal aims to answer four major questions of great significance to cancer and metastasis biology: (i) what is the mechanism of upstream regulation of ApoE by the DNAJA4 heat-shock factor? (ii) How does the binding of ApoE to the endothelial LRP8 receptor suppress angiogenesis? (iii) Could we develop a genetic model of melanoma metastatic progression driven by genetic inactivation of ApoE and use this model to test the anti-metastatic efficacy of an ApoE peptide mimetic? and (iv) does the prevalent human ApoE4 polymorphism drive mouse melanoma metastatic progression. The development of an ApoE inactivation driven genetically initiated model of melanoma metastatic progression is innovative and could beneficially impact the scientific, medical, and pharmaceutical communities-allowing us to test and develop ApoE peptide therapy in an immunoproficient model. Discovery of an unexplored post- transcriptional mechanism that regulates ApoE, a gene implicated in dementia and cardiovascular disease could also have broad scientific and clinical impact and reveal another avenue for therapeutic activation of ApoE. Testing the impact of angiogenic suppression of breast and lung cancer by ApoE- LRP8 could broaden the scope and impact of ApoE therapy to these prevalent cancers as well.